1. Field of the Invention
This invention generally relates to vehicle brake systems. More specifically, this invention relates to controlling the pressure within a vehicle brake system during a traction slip control maneuver. This invention includes a device and methodology for controlling electromagnetically activated relief valves within a vehicle brake system having traction slip control capability, by selectively energizing the electromagnetic component of the relief valve. The relief valve is selectively energized in order to control the maximum pressure obtained during a traction slip control maneuver.
2. The Prior Art
Modern vehicle braking systems include the capability of having antilocking braking action and performing a traction slip control maneuver. Braking systems including traction slip control are typically characterized by the ability to generate a braking force within the braking system independent of the vehicle operator in order to create some desired level of pressure causing the wheel brakes to engage. In this general manner, traction slip control is achieved because the wheels, which would otherwise spin in an undesirable manner not maintaining contact with the driving surface, are prevented from slipping. Braking systems that include traction slip control typically include an auxiliary pressure pump which is motor controlled to create the desired pressure within the braking system in order to complete a traction slip control maneuver. Such auxiliary pressure pumps act independently of the operation of a brake pedal normally associated with the brake system and are typically isolated from the master cylinder of the brake system. Because of the nature of the pressure created by the auxiliary pressure pump for a traction slip control maneuver (TSCM) it is necessary to provide a means for allowing the pressure within the braking system to be relieved when it becomes desirable to end the TSCM. Similarly, it is desirable to relieve the pressure within the braking system in order to maintain a desired pressure for completing the TSCM.
One attempt at maintaining the desired pressure within the braking system during a TSCM includes incorporating mechanical relief valves into the braking system. Conventional mechanical relief valves have several drawbacks and disadvantages associated with them. For example, mechanical relief valves are typically noisy. It is desirable to reduce the amount of noise generated by an automotive braking system in order to increase the vehicle operator's comfort and to enhance the satisfaction of the driving experience. Another drawback associated with including a mechanical relief valve in a traction slip control brake system is that the mechanical relief valves introduce extra hardware that may otherwise be unnecessary. It is desirable to reduce the amount of hardware associated with a vehicle braking system in order to improve system efficiency and diagnostic capabilities, and to make the overall vehicle manufacturing process more efficient.
Another attempt at maintaining the desired pressure within a vehicle braking system that includes traction slip control includes the addition of sophisticated pressure modulators within the braking system. Typical pressure modulators include the drawbacks of being relatively sophisticated and cumbersome and therefore introduce complexity into the braking system that is preferably avoided.
This invention eliminates the need for such mechanical relief valves or pressure modulators and controls the pressure within the braking system during a TSCM by selectively controlling an electromagnetically actuated isolation valve. This invention includes the realization that an electromagnetically actuated isolation valve maintains a holding pressure that is proportional to the amplitude of the energizing current supplied to the valve. Therefore, this invention presents the advantages of reducing the complexity and number of hardware components associated with a traction slip control braking system. Further, this invention improves the braking system function by eliminating the undesirable noise commonly associated with mechanical relief valves. Other advantages provided by this invention include improved system diagnostics and the ability to selectively control the pressure maintained within the braking system during a traction slip control maneuver.